1. Field of the Invention
The present invention relates to a swivel device in which a swivel head having a plurality of tool spindles is provided to be turnable, and also to a grinding machine incorporating the swivel device therein.
2. Discussion of the Related Art
As described in Japanese unexamined, published patent application No. 2000-108026 for example, there has been known a process-intensive cylindrical grinding machine, wherein a wheel head (swivel head) with a plurality of wheel spindles each supporting a grinding wheel is provided to be turnable and wherein the wheel head is selectively turned by a swiveling mechanism to predetermined angular positions so that various kinds of grindings can be performed on a workpiece by the selective use of the grinding wheels.
In the known cylindrical grinding machine described in the Japanese application, one wheel spindle has a straight grinding wheel (G1) at one end thereof and also has an angular grinding wheel (G2) at the other end thereof. For a grinding operation with the straight grinding wheel, the wheel head is turned a predetermined angle about a center shaft (13) to bring the one wheel spindle in parallel relation to a traverse feed direction of a work table. For another grinding operation with the angular grinding wheel, on the other hand, the wheel head is turned another predetermined angle about the center shaft to bring the generatrix of a grinding surface facing a workpiece of the angular grinding wheel into parallel relation to the traverse feed direction of the work table.
In the cylindrical grinding machine of this kind, a swivel drive unit composed of a worm and worm-wheel mechanism for turning the wheel head and a positioning and fixing unit composed of a curved-gear coupling for positioning the wheel head to a designed angular position are arranged to be spaced long therebetween in the vertical direction (the swivel axis direction) of the wheel head. This unavoidably causes the position of the wheel spindle to go far away in the vertical direction from the top surface of a bed of the grinding machine and hence, gives rise to a problem that the wheel head is lowered in rigidity against a rotational moment and is liable to be inclined by the grinding resistance.